Traveling has always been important for people and there has always existed a need to find destinations smoothly, easily and time efficiently. The demand is emphasized by the enormous popularity of the Global Positioning System (GPS) as a tool to find a desired destination. While today's global navigation satellite systems (GNSS) are highly capable, they still only function reliably when the receiver is outdoors; detailed guidance ceases at the entrance to a building. From a technical standpoint, the reason for this gap in coverage is that the GNSS satellite signals are weak and cannot typically penetrate a building exterior and structure.
Nonetheless, there are still times when location guidance inside a building is needed. For example, with respect to larger buildings such as airports, university campuses, hospitals or shopping malls, a user may easily become lost or misdirected, and the need to find a desired destination within the building remains. Thus, with current technology, a traveler might easily find an airport, but cannot receive GPS assistance to find their way from the airport entrance to his or her terminal or gate.
There are two main approaches available for indoor navigation based on different information sources, namely landmark-based navigation and dead reckoning. In landmark-based navigation, indoor landmarks with known position are deployed in the indoor environment, and the user is equipped with a map of these landmarks. The localization algorithm consists in triangulation and trilateration based on detection of one or more of these landmarks. This includes fingerprinting of radio signal strength indications (RSSI) from WiFi, cell phone base stations, or other radio beacons. The advantages of landmark based navigation are that it provides robust, potentially quite accurate, drift-free localization. To realize the approach simple localization algorithms can be utilized, e.g., filter methods are not needed, but can be used to get smooth trajectories. The disadvantages of landmark based navigation are that it requires pre-installed infrastructure and tedious mapping. The approach is sensitive to modification of the mobile radio beacons, their position or other changes of the radio environment.
The other primary approach, dead-reckoning, is based on inertial measurements and map based corrections. The basic principle of dead-reckoning is to integrate speed and course changes to a global course and position. Since velocity and course rate are subject to offsets and disturbances, the integrated position will quickly drift away. An indoor map is then required to stabilize the solution to stay in a feasible set of indoor positions, and to provide feedback of the actual offset values. The advantage of dead-reckoning is that it is a general and well known principle that only involves sensors in the device and no infrastructure. The approach works well in indoor environments with a limited number of alternatives to move (the map is informative). The disadvantage of dead-reckoning is that it requires more complex algorithms, where filtering is required. The approach works less well in open indoor areas, where there is little information in the map. Further, drifts in the position estimate are common. These principles can be combined into one solution that potentially avoids all disadvantages, but such an approach faces many challenges and still requires a complex algorithm.
Nonetheless, since all indoor navigation algorithms require information from a radio receiver and/or inertial sensors, these devices need to be active during the entire time during which navigation occurs. This requires energy, and extensive use will drain the battery quickly. For this reason, a typical device hosting an indoor navigation algorithm is typically not designed for extended use, and the radio and the inertial sensors are not assumed to be active for longer periods, such as a longer visit at an airport, a fair or shopping mall. In the event that extended use is desired, power management is a crucial challenge.
It will be appreciated that this background section discusses problems and solutions noted by the inventors; the inclusion of any problem or solution in this section is not an indication that the problem or solution represents known prior art except as otherwise expressly noted. With respect to prior art that is expressly noted as such, the inventors' summary thereof above is not intended to alter or supplement the prior art document itself; any discrepancy or difference should be resolved by reference to the prior art document itself. It will be further appreciated that solving the noted problems, while desirable to the inventors, is not a limitation of the appended claims except where expressly noted, since the claimed invention is susceptible to a wide variation in implementation techniques.